Com 1 transmit nothing but static

[bradp]

Hi  - cross posted from my question at beechtelk.  Having issues with transmit on a 430W.  Thanks. Brad

Hi all,

I’ve been having some intermittent issues with my com1 that just turned constant and am wondering if I need additional troubleshooting steps prior to having it benched at the avionics shop. 

It’s a 430W bought used three years ago. Audio panel is a PMA 8000BTi. About a month an a half ago I noticed some random radio static making my side tone cut in and out on com1. Yesterday was flying out of Dulles (Murphy’s law tested and still the law of the land) and my Com 1 essentially went TU for transmit with the same symptom. Relied on a 40 year old KX-170b during departure and coming home today I get nothing but static when I try to transmit.  

Symptoms:
- harsh / loud static cutting in and out (also cutting my side tone in and out) when I try to transmit on com1 
- occurs when trying to transmit from either pilot or co pilot position 
- Carrier with harsh static reaches ATC (thanks Washington center for verifying that)


Pertinent negatives:
- receive works perfectly fine on Com1
- occasionally the side tone works fine and I am heard 5x5 by ATC. This is an exception now and not the rule 
- not associated with electronic devices or chargers
- pulled each breaker on the ground today and no change in symptoms (ie not alternator or another EMI / RF bleed source)
- does not change with mag selector positioning ignition including off  
- doesn’t seem associated with a particular frequency although changing frequency used to seem to help

Troubleshooting steps taken so far
- turned audio panel off to enable the emergency/bypass mode - still have the static issue on Com 1 according to ATC 
- when the problem was intermittent, i had tried both a lightspeed and halo headset (I’ve heard of halos causing issues) and no difference. 

Troubleshooting steps to be taken prior to bench and / or swap with another unit 
- reseat boxes
- check grounds at 430W, pin continuity / resistances 
- swr antennas and / or swap antennas to see if problem tracks with antenna 
- swap audio panel (thinking it’s not the audio panel since static occurs with audio panel in bypass mode)
- swap 430 (if I can find a willing local pilot or shop)

Did I lose an antenna ground? RG400 or another connector disrupted / pinched? Transmit module on the 430W? Heat related issue? 

Thanks for the help

Brad

 

[jaylw314]

also check the mic jack and wiring on the pilot side?  Maybe some contact cleaner in the jack itself?

You can reseat the boxes yourself (preventative maintenance).

[bradp]

BNC connector at antenna tested bad - conductor was shorted to shield.   Connector got replaced.  Ground checks good.  We’ll do a flight test tomorrow.  One more item on the list of things that can go wrong I guess....

[jaylw314]

21 minutes ago, bradp said:

BNC connector at antenna tested bad - conductor was shorted to shield.   Connector got replaced.  Ground checks good.  We’ll do a flight test tomorrow.  One more item on the list of things that can go wrong I guess....

It's always nice when it's a cheap fix  

[201Steve]

3 hours ago, bradp said:

BNC connector at antenna tested bad - conductor was shorted to shield.   Connector got replaced.  Ground checks good.  We’ll do a flight test tomorrow.  One more item on the list of things that can go wrong I guess....

How does one test said connector? I have a similar problem on my com2. Zero radio experience but trying to learn. 

[Yetti]

3 hours ago, bradp said:

BNC connector at antenna tested bad - conductor was shorted to shield.   Connector got replaced.  Ground checks good.  We’ll do a flight test tomorrow.  One more item on the list of things that can go wrong I guess....

Ha I was thinking that when I was reading the description.  sloppy techs.   Reason number 28 for the Flush cut Snap on pliers.   If you go around with them and clean up the little stragler grounds they don't do that.

https://store.snapon.com/Standard-Diagonal-6-Diagonal-Flush-Cut-Cutter-P886048.aspx

[Yetti]

15 minutes ago, 201Steve said:

How does one test said connector? I have a similar problem on my com2. Zero radio experience but trying to learn. 

disconnect both ends of cable.  Should get 0 ohms on your VOM.   Will also show up with SWR meter.

[Bob_Belville]

Ha I was thinking that when I was reading the description.  sloppy techs.   Reason number 28 for the Flush cut Snap on pliers.   If you go around with them and clean up the little stragler grounds they don't do that.
https://store.snapon.com/Standard-Diagonal-6-Diagonal-Flush-Cut-Cutter-P886048.aspx

I picked up a pair at SnF. A must have, but I paid a lot less than Snapon gets.


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[RLCarter]

1 hour ago, Yetti said:

Ha I was thinking that when I was reading the description.  sloppy techs.   Reason number 28 for the Flush cut Snap on pliers.   If you go around with them and clean up the little stragler grounds they don't do that.

https://store.snapon.com/Standard-Diagonal-6-Diagonal-Flush-Cut-Cutter-P886048.aspx

Yep, I only cut smaller gauge electrical wire and zip ties with them

[bradp]

I need to get a pair maybe at Osh.  I have the ones from stein website.  This is literally my most used and useful tool - I like the ones I have but they do get some use and replaced with some frequency.  

Interestingly - there was a tiny little strand of errant ground that had coarsed through the dielectric.  I’m going to chock it up to manufacture defect and me having recently  manipulated the end of the connector when I  tested SWRs for both antennas when my other radio (kx-170b) died.  When the bad connector was cut off the blunt end conductor was still shorted to ground.  WTF.  The other end connector was rechecked and wiggled a lot - still tested fine.  The course of the wire was traced without apparent damage or kinks.  Back to the problem end - cable trimmed back a few inches fixed the short. 

Small clarification on yeti statement above.  There should be infinite resistance between the center conductor and ground normally.  If it’s shorted to ground there’s 0 ohm / resistance.   SWR did improve from 1.5 to 1.2 by fixing the connector.  When RG-400 (preferred for all our applications over the old RG-58) is terminated the conductor is tested against the shield with an ohm meter after each step to make sure there is no alternative path for the conductor.  

Here’s the super easy digital SWR I’ve been using.  Also among my favorite pieces of kit.  Clearly not EE grade but gets the job done and comes with BNC adapters and some dummy loads.  Easy to read for my increasingly bifocal needing eyes.  Cheap and decent for a quick antenna check.

https://www.amazon.com/Gam3Gear-SURECOM-125-525-Digital-Handheld/dp/B075H8FDDR/ref=mp_s_a_1_9?keywords=digital+swr+meter&qid=1561700642&s=gateway&sprefix=digital+swr&sr=8-9

 

[Yetti]

The other reason for the flush cuts is they do a better job at initially cutting the shield by creating a straight line with no errant strands. Last BNCs connections I made I still soldered them.  Don't have to worry about corrosion like you do with a crimp.   it's tricky to do a good solder job, because it's just the right amount of heat to melt the solder, but not melt the insulator. Old weller hot guns do the best job at this.   Solder makes them last for decades. We used to have solder all the PL259s.  Then used a military crimper thing, but there was only one crimper and it did not go to the field so you still had to be able to solder the connectors in the field.

We used to do 3 or 4 trucks a day with new radios so, the price of a good cutter did not matter as much as having to redo the job.  And the Snap-on were the best.   The bad thing is the tip of the cutter will break if you drop them.  Both pairs of mine have a broken tip.  

[bradp]

The new connector was soldered :-) 

[Yetti]

3 hours ago, bradp said:

The new connector was soldered :-) 

there you go.